1. Field of the Invention
The present invention relates to a motion converting device and an impact absorbing/buffering device, and in particular, to a motion converting device which converts one of linear motion and rotational motion to the other, and to an impact absorbing/buffering device which includes the motion converting device.
2. Description of the Related Art
Conventional examples of devices which convert rotational motion to linear motion are a robot actuator (Japanese Laid-Open Patent Application (JP-A) No. 61-127015) which includes a nut joined to a shape memory effect alloy wire and a screw rotary shaft (ball screw) engaged with the nut, and a linear actuator (Japanese Laid-Open Patent Application (JP-A) No. 7-46789) which uses a mechanism for converting rotational motion into linear motion by rotating a motor and winding up a flexible, tape-shaped sheet body.
However, in order to convert rotational motion to linear motion, the robot actuator uses the nut and the screw rotary shaft (ball screw), and has a sliding joint portion. Further, the linear actuator has a sliding surface between sheets, and further, cannot convert linear motion to rotational motion.
When a sliding portion is used, there arise problems such as noise, wear, backlash, and friction loss. Further, sliding portions require maintenance with lubricating oil. Therefore, sliding portions cannot be used in special environments such as in certain medical facilities in which oil and the like should be avoided for sanitary reasons, or in outer space where there is a low-gravity environment. Accordingly, the range of application is limited. Further, when motion is being converted, the nut, the screw rotary shaft and the like must be slid, and thus a load is not transmitted smoothly.